830 Transactions of the Societtj. 



to regulate the sound. In such a case there would not be much 

 difference between the organs of hearing in the male and female. 

 But if one sex attracts the other by smell, it is not necessary that 

 the attractive sex (female in this case) should have well developed 

 organs of smell. If the antennules were hearing organs, I still 

 do not see how they would be available for bringing the sexes 

 together, for the assumption that the male can produce any sound 

 is pure hypothesis, and so soft are the parts of its body that I 

 doubt whether such a thing is possible ; indeed the whole evidence 

 is so strongly in its favour that Sir John Lubbock's conclusion is 

 evidently the right one. 



The eye is a most beautiful organ. If viewed laterally (Fig 1, a) 

 it appears globular, but is not really so. Seen from beneath (Fig. 11) 

 it is found to be reniform, composed of a series of cuneiform 

 crystalline tubes (Fig. 11, Z^) with rounded extremities, but not so 

 closely appressed as to become hexagonal. These are enclosed in a 

 very transparent membrane (Fig. 11, a), and radiate from a dark- 

 coloured pigment mass (c) in which their inner ends are embedded. 

 This eye is remarkable for exhibiting a distinct tendency to become 

 two eyes as in the higher Crustacea. Down the centre of it 

 (Fig. 11) there is drawn a faint line, which in the lower half 

 widens into a considerable gap, where there are no crystalline tubes, 

 the right and left halves thus formed corresponding to the right 

 and left cerebral ganglia (Fig. 11, e and /). In some specimens 

 this gap is much more distinct than in the one figured. We see the 

 same thing in the larva (Zoea) of the prawn, which has one eye, 

 but later on two eyes. The eye of Leptodora too, is much in 

 advance of that of the other Cladocera, in which it consists of a 

 pigment mass with a few irregular crystalline sacs attached to it. 

 Between the upper and lower ganglia of the brain there are several 

 dark oval bodies (Fig. 11, i), whose function I cannot guess. 

 The basal ganglion gives off a large commissure {h), which 

 bifurcates, in some specimens close to, in others at a considerable 

 distance from its origin ; the two halves being very much thickened 

 as they pass one on each side of the oesophagus to form the 

 oesophageal collar (Fig. 2, x). They meet on the opposite side, in 

 a large nerve mass formed by the coalescence of all the nerve 

 centres of the thorax and abdomen into one. This mass is situated 

 between the bases of the six pairs of legs and the mandibles, and 

 gives off nerves, one to each leg, one to each side of the abdomen, 

 and one larger than the others to each antenna. These nerves of 

 course give off smaller branches innumerable, but I need not 

 describe them further than to say that every individual seta is 

 provided with one. In the large setae on the antennary branches 

 (Fig. 4, a) the nerve terminates on the diaphragm between the 

 two joints. 



